Topic: Cylinder head removal CB750

[RupertB]

Here's the point when you find out who your friends are! - Now then, I tried to remove the cylinder head of my 74 K4 750 motor and ended up removing the head and barrels together which isn't a problem as the whole lot is coming to bits anyway, but I now have to separate the head fromthe barrels obviously.
The fins bear witness to a previousowner who has used the time-honoured 'tyre lever and brute strength' method, but I'd rather avoid that for obvious reasons!
I have removed all the nuts including the ones that sit in by the spark plugs, and also removed the bolts front and rear in the centre of the block, but there are meant to be a few other bolts somewhere in the head, looking at the Clymer manual they seem to be under the rubber bungs under the cam blocks. However looking beneath those bungs the bolts seem to be missing so - do I go for a bit of leverage and hope, or are there more hidden bolts I should look out for? And even when all bolts and buts are removed, is the head sticky to get loose?
Good news is that the pistons are 74mm so I have an 810 Yoshi engine. Rumour turns to fact - hurrah!

[gnarlycharlie4u]

I hate to bump an old topic but I'm having a similar problem. PO seems to have glued the crap out of the cyl to head gasket so now I'm pretty clueless as to how to separate the two. I've tried being gentle (rubber mallots, pieces of wood, plastic prypar) but nothing seems to be even making a dent.

Any suggestions?

[bollingball]

There are a couple of stronger pry points on the rear of the head look for two little tabs on the head just below the intake ports they line up where the bolts go through the jugs this is the strongest pry point. If you don't buy another tool you should consider HondaMans book it covers this and a ton more tricks that you usually only get with time.

[gnarlycharlie4u]

There are a couple of stronger pry points on the rear of the head look for two little tabs on the head just below the intake ports they line up where the bolts go through the jugs this is the strongest pry point. If you don't buy another tool you should consider HondaMans book it covers this and a ton more tricks that you usually only get with time.

I tried those pry points already but the thing just isn't budging. RTV is some strong ish apparently. I do definitely need to get hondaman's book. I wish I bought it when it came out like I planned to.

Maybe I just need to stop pussyfooting around and give it some serious force.

[RupertB]

My project has gone on hold until I have enough money to make a substantial move forward on it, but it is at a point with the top end now stripped and everything (fairly) neatly boxed and sorted. I did eventually get the head off but it wa unusual - I treble and quadruple checked I really really had got every bolt removed, and with gentle prying and leverage round and round the base of the head - more times than I can remember - got one end of the head to lift away, but every time I went to work on the other end the freed and sat back down again. So I put a thin lath of wood through over cylinder number three, then managed to slide a ratchet strap inboard of that, before lifting the strap just enough to let the weight of the block pull on the joint. With a little more gentle (and I mean really gentle) leverage with wood rather than metal (because thin wood breaks first when you lose your temper!) it eventually separated. I think the biggest stick point was actually the round hollow peg thing which looks like an oilway, but my engine hasn't run for over 15 years, so there ain't no oil in there!
If you are still awake after that - hope it helps!

[OldSchool_IsCool]

Hmmmm maybe heat 'em up pretty good in ur oven (plan on a day when the Mrs is out).  If that doesn't free them up, try to draw a fine guitar string through the joint.  If all the bolts are out, there shouldn't be any metal to prevent the string from passing through.  Take care not to "saw" with the string, just try to push it through when hot.

[srook]

You can also try to use cedar shims.  If you can get one started you can pound it in which will drive the head and barrels apart without damaging the gasket surfaces.
Scott

[markb]

I would double check to make sure the four bolts under the rubber pucks aren't there.  There's only four of them under the six pucks and sometimes they're hard to see.  It's hard to believe that someone would do that rebuild and "forget" to put them in.  It can't hurt.   

[MCRider]

I use the tiniest of chisels as a wedge. A 1/4 inch hardened chisel, tap it into the head gasket area till you hear the head separate then work around. All obvious caveats, all bolts out etc.

Also I'm thinking a heat gun couldn't hurt.

[gnarlycharlie4u]

I'm wondering if sticking it in the freezer would help any?

[MasterChief750]

Hmmmm maybe heat 'em up pretty good in ur oven (plan on a day when the Mrs is out).  If that doesn't free them up, try to draw a fine guitar string through the joint.  If all the bolts are out, there shouldn't be any metal to prevent the string from passing through.  Take care not to "saw" with the string, just try to push it through when hot.

theres aligning pins(lack of a better word) between the barrel and head. i ended up trying to pry but it failed miserably and cracked a fin. i ended up dropping it about a foot onto a carpet pad on the concrete and it came apart

[gnarlycharlie4u]

Hmmmm maybe heat 'em up pretty good in ur oven (plan on a day when the Mrs is out).  If that doesn't free them up, try to draw a fine guitar string through the joint.  If all the bolts are out, there shouldn't be any metal to prevent the string from passing through.  Take care not to "saw" with the string, just try to push it through when hot.

theres aligning pins(lack of a better word) between the barrel and head. i ended up trying to pry but it failed miserably and cracked a fin. i ended up dropping it about a foot onto a carpet pad on the concrete and it came apart

Yea I broke a fin too... I suppose I might as well try the drop since I have nothing to lose.

[MasterChief750]

thinking back i tried the drop for a bit then ended up holding the barrels and hitting it against the ground

[gnarlycharlie4u]

thinking back i tried the drop for a bit then ended up holding the barrels and hitting it against the ground

I've tried setting it on it's side on the bench with the cyl hanging off. Then put a foot on it to stabilize it and smacked it with a plastic maillot till I broke the maillot :-/

[RupertB]

I can't see heat hurting as long as it isn't too localised, and I can't see cold being a problem with the same caveat.
My engine had been put together without the bolts under those rubber bungs which is pretty ignorant, but then I don't know if it has actually run since then or not.
I lke the guitar string idea - I think some persistent gentle prying with a thin chisel, or maybe a feeler gauge perhaps? I unintentionally started getting it to lift at one end and had the dangerous but useful extra facility of leverage the length of the block, but the possibility was always there of bending those locating lug/tube things.
Don't know if I fancy dropping it from any height, even onto carpet. Sounds a bit too much 'sh*t or bust', with too great a likelihood of 'sh*t' than I would like.
Good luck anyway!
Keep us posted please.

[gnarlycharlie4u]

update: cyl head is removed. I just went at it with a LOT of pbblaster, atf, brake cleaner, and a putty knife.

verrrrrrrrrrry gradually

[RupertB]

Hurrah! Doesn't it seem obvious when it is done, but impossible before. Machines 0, Humans 1.

[gnarlycharlie4u]

Hurrah! Doesn't it seem obvious when it is done, but impossible before. Machines 0, Humans 1.

yea painfully obvious. actually that was my original thought but I couldn't find a good clean putty knife that wouldn't score the head

[MasterChief750]

oh jjust a little tip. get a can of carb dip and put it in a pan ad soak the gasket surfaces on the jugs and head in it. makes the old gasket a million times easier to get off.

[fmctm1sw]

Hurrah! Doesn't it seem obvious when it is done, but impossible before. Machines 0, Humans 1.

We were already down 1-0 after I scratched up a 550 top end trying to get it apart 

[gnarlycharlie4u]

oh jjust a little tip. get a can of carb dip and put it in a pan ad soak the gasket surfaces on the jugs and head in it. makes the old gasket a million times easier to get off.

I of course didn't find any pans big enough until AFTER I got the mofo off. haha.

[stueveone]

Figured I'd post what worked for me:
I used a wonder bar in between the cylinder and head and twisted it with an adjustable wrench rather than prying it up and down. After about 2.5 hours trying other methods, I was shocked how easy this worked (though I'm sure the dead blow probably loosened it a little!)

[HondaMan]

I use a very sharp knife and slice the head gasket into 2 layers, and pull them apart as I go.

[chewbacca5000]

Here's the point when you find out who your friends are! - Now then, I tried to remove the cylinder head of my 74 K4 750 motor and ended up removing the head and barrels together which isn't a problem as the whole lot is coming to bits anyway, but I now have to separate the head fromthe barrels obviously.
The fins bear witness to a previousowner who has used the time-honoured 'tyre lever and brute strength' method, but I'd rather avoid that for obvious reasons!
I have removed all the nuts including the ones that sit in by the spark plugs, and also removed the bolts front and rear in the centre of the block, but there are meant to be a few other bolts somewhere in the head, looking at the Clymer manual they seem to be under the rubber bungs under the cam blocks. However looking beneath those bungs the bolts seem to be missing so - do I go for a bit of leverage and hope, or are there more hidden bolts I should look out for? And even when all bolts and buts are removed, is the head sticky to get loose?
Good news is that the pistons are 74mm so I have an 810 Yoshi engine. Rumour turns to fact - hurrah!

I just got done taking the head off my 1973 CB750 and had a heck of a time getting 2 of those little outside screws out from under the rubber bungs. On the head I have 10mm won't fit down there.  Had to use vice grips, screwdriver and a rubber mallet.
Trust me they are there.  They may be covered with grease and dirt, but they are there.  With all the bolts out and a few taps of a rubber mallet the head came right off.  I would keep hunting for more fasteners.  I don't know how many times I have tried to remove an oil pan and missed that one bolt holding a cable and my pan would not come off.

Good Luck!

[MCRider]

Danger Will Robinson!

Yes there are 4 in a row under the #1,3,4,and 6 biscuits.

These should be removed BEFORE removing the head nuts. Once the head nuts are removed the swell of the gasket and the cylinder head serve to increase the torque on those dudes tremendously. To the point where you can barely, if even, get them out. You may want to consider reinstalling the cyl/head assy, onto its studs, tighten the nuts back down, then remove the 4 under the bungs.  This can be done easily with the pistons off.

If you have a long Phillips bit, you could use an impact driver on them.

[gnarlycharlie4u]

Danger Will Robinson!

Yes there are 4 in a row under the #1,3,4,and 6 biscuits.

These should be removed BEFORE removing the head nuts. Once the head nuts are removed the swell of the gasket and the cylinder head serve to increase the torque on those dudes tremendously. To the point where you can barely, if even, get them out. You may want to consider reinstalling the cyl/head assy, onto its studs, tighten the nuts back down, then remove the 4 under the bungs.  This can be done easily with the pistons off.

If you have a long Phillips bit, you could use an impact driver on them.

Impact driver works but it's hard to find one that long.
I still prefer using a deep socket. It's made short work of 3 motors so far.

[john campling]

Here's what I did
Took the head and barrels off together as it quickly became obvious it was not going to give up without a fight.
Cut some 60mm mdf disks which slotted in the bores like mdf pistons, just to protect the top of the combustion chamber.
Planed a bit of wood to fit in the bore and hit it with a hammer. The problem was getting enough grip to stop it moving so I ratchet strapped it to the bench so it was resting on the wood and the carb inlets. I thought this might be enough to split it , not quite. So I gave a few taps with a hammer on the wood in the bore and off it popped.

[Romhog]

good one! never ever thought of putting an adjustable wrench on my wonder bar! great torque with that !  thanks for sharing!

Figured I'd post what worked for me:
I used a wonder bar in between the cylinder and head and twisted it with an adjustable wrench rather than prying it up and down. After about 2.5 hours trying other methods, I was shocked how easy this worked (though I'm sure the dead blow probably loosened it a little!)

[AgPete139]

These should be removed BEFORE removing the head nuts. Once the head nuts are removed the swell of the gasket and the cylinder head serve to increase the torque on those dudes tremendously. To the point where you can barely, if even, get them out. You may want to consider reinstalling the cyl/head assy, onto its studs, tighten the nuts back down, then remove the 4 under the bungs.  This can be done easily with the pistons off.

If you have a long Phillips bit, you could use an impact driver on them.

Since I'm not the sole one reviving this thread, I will shine some light as well.

My #3 Phillips screwdriver started to strip the heads of the 4 bolts underneath the "condom" bungs. Like McRider stated, take these off FIRST before the cam nuts. (I didn't, but I learned now.)

I happened to have a cheap-o socket set from years ago, and the cheaper sets have thin walls. If you can find a thin-walled 10mm socket with an extension, do this. I practically stripped the head of one Phillips bolt.

Procedure:

• Let soak with PB Blaster or penetrating oil.
• Phillips screwdriver into bolt. Give a few solid (NOT Hulk strength) taps (to shock the threads) with a metal hammer.
• Put thin-walled socket on bolt. Use a large extension on your socket wrench. (or breaker bar)
• Remove bolts. Continue to turn, even though they feel like they will not give. They will.

NOW, as far as remove the cylinders (jugs) and the heads, I am currently at a loss. The gasket material is still soaking since yesterday, and I will try later today with a putty knife. Minor tapping with a thin wooden wedge will also be used.


Rubber Mallet Usage:
After reading so many other people's anecdotes, I attempted to hit it with a medium-soft polyurethane mallet.

BEWARE: If you do this, ONLY strike the top head. Hit it directly, in a flat manner. You can break the fins of the head. MORE LIKELY, is that you will break off pieces of the brittle cylinder fins instead. They don't bend, they only break. These are a lot thinner, and you can accidentally bump them while trying to remove the head. I found out the hard way. I will JB Weld it back on though and black paint over the entire part.



Good luck to future readers.

[JerrodR]

Replacing a head gasket, and am running into the same issue. I'm considering taking a propane torch and heating along the gasket line to hopefully melt some of the glue, and loosen things up a bit..

[MRieck]

Replacing a head gasket, and am running into the same issue. I'm considering taking a propane torch and heating along the gasket line to hopefully melt some of the glue, and loosen things up a bit..

Sometimes only bead blasting or vapor blasting will clean the surface.

[HondaMan]

Replacing a head gasket, and am running into the same issue. I'm considering taking a propane torch and heating along the gasket line to hopefully melt some of the glue, and loosen things up a bit..

In the old days (before I had a wife who protects her oven from people like me) I would put the stuck-together top ends in the oven at 200-250 degrees for about 20 minutes. This softens the sealant in the old head gaskets. Then I'd take them out (with winter gloves!) and start the prying, they usually separated right away.

Now I have to leave them out in the Colorado sun, which only gets them up to about 120 degrees on a hot summer's day...